1. Field of the Invention
In an image forming apparatus for forming an image electrophotographically by transferring a developed image formed on an image bearing member to a transfer medium, the present invention relates to a cleaning device for removing residual developer (residual toner) remaining on the image bearing member by using a cleaning blade.
2. Description of the Related Art
In conventional image forming apparatus such as electrophotographic copiers or printers, an image is formed by performing a series of steps consisting of: a charging step for uniformly and evenly charging an image bearing member, for example, an electrophotographic photoconductor drum; an exposing step for writing an electrostatic latent image to the photoconductor drum; a developing step for developing the electrostatic latent image with toner which is a developer; a transfer step for transferring the developed toner image to paper which is a transfer medium; a fixing step for fixing the transferred toner image to the paper; and a cleaning step for removing residual toner, etc. remaining on the photoconductor drum to prepare for the next cycle of image formation.
Usually, the untransferred toner (residual toner) left on the photoconductor drum from the transfer step is removed using a cleaning blade or a cleaning brush in the cleaning step, and the toner removed from the photoconductor drum is directed from the cleaning device to a toner container for recovery. Previously, the recovered toner was disposed as industrial waste.
However, in recent years, in order to reduce the running costs of image forming apparatus, designs that can extend the lives of components of the apparatus have been studied and commercially implemented.
As an example, Japanese Unexamined Patent Publication JP-A 9-251264 (1997) discloses a toner recycling-type image forming apparatus in which, of the residual toner cleaned off the photoconductor drum, only the toner charged with the polarity proper for development is collected and supplied for reuse into a developing unit for developing an electrostatic latent image on the photoconductor drum.
The cleaning device of the image forming apparatus disclosed in Japanese Unexamined Patent Publication JP-A 9-251264 comprises: a conductive brush roller which is supplied with a bias voltage of the same polarity as the proper polarity in order to remove, from the residual toner on the photoconductor drum, the toner charged with the polarity opposite to the polarity proper for development; a roller-like electrode disposed in contacting relationship to the brush roller and supplied with a bias voltage of the opposite polarity to that applied to the brush roller; and a rubber blade for scraping off the toner adhering to the roller-like electrode.
In operation, the oppositely charged toner is removed using the conductive brush roller by electrostatically attracting such toner away from the photoconductor drum, the toner adhering to the conductive brush roller is electrostatically attracted to the roller-like electrode, and the toner adhering to the roller-like electrode is removed using the rubber blade.
However, according to the above construction, if the developer is a two-component developer consisting of toner and carrier, not only the toner but also the carrier is made to adhere to the photoconductor drum; in particular, in the case of an apparatus employing a reverse development method (the method that makes toner adhere to exposed areas as image areas), if the carrier adhering to the photoconductor drum is removed by the conductive brush roller, it is difficult to completely remove the carrier electrostatically adhering to the conductive brush roller by using the roller-like electrode contacting the end of the conductive brush roller, and as a result, the carrier not removed but left adhering to the conductive brush roller is again adhered to the photoconductor drum, causing a degradation in image quality.